Increased Expression of the Auxiliary β2-subunit of Ventricular L-type Ca2+ Channels Leads to Single-Channel Activity Characteristic of Heart Failure

Roger Hullin,Moritz Bünemann,Paul Mohacsi,Eva Schmitteckert,Lutz Hein,Jan Matthes,Arnold Schwartz,Stefan Herzig,Sibylle Von Vietinghoff,Ilona Bodi,Dennis Rottländer,Ralf Gilsbach,Uta C Hoppe,Ismail Friedrich Khan,Marta Rubio,Karen D'Souza

doi:10.1371/journal.pone.0000292

Abstract

BackgroundIncreased activity of single ventricular L-type Ca2+-channels (L-VDCC) is a hallmark in human heart failure. Recent findings suggest differential modulation by several auxiliary β-subunits as a possible explanation.Methods and ResultsBy molecular and functional analyses of human and murine ventricles, we find that enhanced L-VDCC activity is accompanied by altered expression pattern of auxiliary L-VDCC β-subunit gene products. In HEK293-cells we show differential modulation of single L-VDCC activity by coexpression of several human cardiac β-subunits: Unlike β1 or β3 isoforms, β2a and β2b induce a high-activity channel behavior typical of failing myocytes. In accordance, β2-subunit mRNA and protein are up-regulated in failing human myocardium. In a model of heart failure we find that mice overexpressing the human cardiac CaV1.2 also reveal increased single-channel activity and sarcolemmal β2 expression when entering into the maladaptive stage of heart failure. Interestingly, these animals, when still young and non-failing (“Adaptive Phase”), reveal the opposite phenotype, viz : reduced single-channel activity accompanied by lowered β2 expression. Additional evidence for the cause-effect relationship between β2-subunit expression and single L-VDCC activity is provided by newly engineered, double-transgenic mice bearing both constitutive CaV1.2 and inducible β2 cardiac overexpression. Here in non-failing hearts induction of β2-subunit overexpression mimicked the increase of single L-VDCC activity observed in murine and human chronic heart failure.ConclusionsOur study presents evidence of the pathobiochemical relevance of β2-subunits for the electrophysiological phenotype of cardiac L-VDCC and thus provides an explanation for the single L-VDCC gating observed in human and murine heart failure.

Highlights

Homeostasis of intracellular Ca2+ concentration [Ca2+]i is essential for cardiac function and integrity; its dysregulation is a hallmark of advanced heart failure [1,2]
The changes of peak current, fraction of active sweeps and open probability mirror findings obtained from single L-VDCC measurements in human cardiomyocytes from non-failing or failing idiopathic dilated cardiomyopathy (DCM) hearts, respectively [6] (Table 1)
In a previous study [6] we found single-channel activity to be significantly increased in ventricular myocytes from human hearts failing due to idiopathic dilated cardiomyopathy compared to non-failing ventricles

Summary

Introduction

Homeostasis of intracellular Ca2+ concentration [Ca2+]i is essential for cardiac function and integrity; its dysregulation is a hallmark of advanced heart failure [1,2]. Chen et al [7] showed attenuated ICa increase by (S)-BayK8644 in human failing myocardium whereas basal whole-cell currents were unchanged, indicating that singlechannel activity is enhanced while channel density is lowered. These findings confirm the idea of an ‘‘electrophysiological heartfailure phenotype’’ of single L-VDCCs. The biochemical nature of this change in phenotype has not been delineated, phosphorylation [8,9] and dephosphorylation [10,11] have been implicated. Our study presents evidence of the pathobiochemical relevance of b2-subunits for the electrophysiological phenotype of cardiac L-VDCC and provides an explanation for the single L-VDCC gating observed in human and murine heart failure

Methods

Results

Conclusion